Heretofore, deflection yoke separators are used for domestic televisions and a display of computers. As the material for the separators, (1) modified polyphenylene oxides (hereinafter referred to as modified PPO), (2) polybutylene terephthalate resins blended with a flame retardant and glass fibers (hereinafter referred to as PBT blended with flame retardant and glass fiber), and (3) polypropylene resins blended with a talc and flame retardant are used.
Modified PPO has a defect that the cost of final products is high based both on the cost of material and the productivity at molding, whereas it is widely used as the material for deflection yoke separators for domestic televisions and a display of computers.
PBT blended with a flame retardant and glass fibers has a defect that it is inferior in tracking resistance. If the tracking resistance is poor, when televisions are used in an environment of a high temperature and a high humidity, outside surface of the deflection yoke separators humidified and covered with dust is partially carbonized by a minute electric discharge to electrically continue thereby producing an inferior insulation. This deterioration in the tracking resistance is caused by the molecular structure of resins used as the material. For instance, since the bond between carbon atoms in benzene ring is strong, such resins as PBT having benzene ring within the molecule are hardly gasified by the heat energy of the minute electrical discharge, and free carbon atoms in the graphite structure remain on the surface to facilitate the electrical continuing thereby decreasing the tracking resistance. On the other hand, polypropylene resins are considerably excellent in the tracking resistance since they do not have benzene ring in the molecule. Accordingly, polypropylene resins are most suitable as the material for deflection yoke separators from the viewpoint of the tracking resistance.
Polypropylene resins blended with a talc and flame retardant are materials which improved the tracking resistance of the PBT blended with a flame retardant and glass fiber mentioned above. In the materials, a halogen-containing flame retardant, decabromodiphenyl ether, dodecachlorododeca-hydrodimethanodibenzodichlorooctene, or their mixture is used as flame retardant.
However, they have a problem that a mechanical property (tensile strength) decreases due to the use of the halogen-containing flame retardant. Further, when they are used at a high temperature, flame retardancy decreases and appearance of final products deteriorates since the flame retardant is bloomed (phenomenon of separation, in a powder-like form, on the surface of final products). Specifically, when deflection yoke separators are injection molded by using a polypropylene resin composition blended with a talc and a flame retardant, the halogen-containing flame retardant mentioned above is bloomed onto a mold (phenomenon of separation, in a powder-like form, on the surface of a mold), the bleeded ingredient adhered on the surface of the mold is transferred on the surface of molded articles, and thus the appearance of deflection yoke separators deteriorates. Besides, the productivity extremely decreases since the production is discontinued and a work for wiping off the bleeded flame retardant is conducted to obtain final products having a good appearance,.
Whereas ethylene-vinyl acetate copolymers (EVA), aliphatic carboxylic acids, or salts of aliphatic carboxylic acids are generally used as additive for suppressing the bleeding phenomenon mentioned above, there exists a problem that a mechanical property (rigidity) decreases and the cost of the material increases.
An object of the present invention is to solve the problems in the prior art mentioned above, and to provide crystalline polyolefin resin compositions which are balanced in cost, and every characteristics of moldability, mechanical properties (tensile strength and rigidity), impact resistance, electrical properties, and flame retardancy, and which avoid the production of inferior appearance of molded products such as deflection yoke separators due to the bleeding of the flame retardant onto the mold when propylene resins blended with a talc and flame retardant are molded, and avoid the decrease in the productivity; and to provide electrical insulating parts comprising the composition.